Child Sex Abuse in the Catholic Church
The main theme of the movie is pedophilia within the Catholic church. At the beginning of their investigation, the Spotlight team are told by church leaders that there are a few bad apples making the barrel look bad, but that pedophilia is not something that is common within the priesthood as a whole. When they start to investigate more deeply, though, the team find that they have been misled, and that pedophilia within the priesthood is actually very common, but also ignored, or covered up. It is also frequently minimized; by dismissing the cases as "a few bad apples" the church authorities suggest that the molestation of only a few children is acceptable, rather than exhibiting outrage that any incidents of it happened at all.
Church Cover Up
Once the team find out that pedophilia within the priesthood is far more prevalent than they have been led to believe, they also discover that great efforts are made to cover this up. Far from being ignorant of the incidences of sexual abuse, church elders and dignitaries are well aware of it, and go to enormous efforts to hide it from the public. The cover up is extensive and goes as high as it possibly can do; not only is Cardinal Law, in Boston, aware of the abuse, but so is the Pope; the order to cover up what is happening comes from the highest authority in the church, which leads the team to realize that there is a conspiracy of silence shielding the priests involved.
There is also a tendency within the church to deny the criminality of this abuse, because the perpetrators are priests. There is a tacit belief that priests cannot be criminals, and therefore what they are doing is not criminal.
Assumptions
There are several assumptions made by the public about priests. The chief one of these is that they are celibate. In reality around eighty per cent of priests are actually involved in relationships. In the film, it can also be seen that the church have managed to perpetuate the assumption that cases of pedophilia are greatly exaggerated; that adults jump on the bandwagon and claim abuse in their past, or that greedy lawyers want to cause trouble by claiming that there are more cases of sexual abuse than is actually accurate.
The film shows the danger in these assumptions and even the Spotlight team are initially examples of this. They assume that the church authorities are telling them the truth when they claim that a few bad apples contaminate the barrel; it is only when they ignore their original assumptions that they start to get to the truth.